Japan quake a 'perfect analog' for what one would look like on B.C. coast

Local residents walk past debris, including an overturned fishing boat, in the town of Minamisanriku in Miyagi prefecture on March 12, 2011 a day after a massive 8.9 magnitude quake and tsunami hit the region.Photo by
Yomiuri Shimbun

VANCOUVER — Like many on Friday, SFU earthquake expert John Clague watched with a mixture of fascination and horror as Japan struggled to cope with the devastation caused by a 8.9 earthquake that sparked an equally destructive tsunami that killed hundreds.

While the images of burning buildings and floating cars were impressive, it was something else, a little closer to home, that kept the professor of earth sciences monitoring the headlines throughout the day. What if the big one hit here?

Like Japan, the West Coast of B.C. rests on a subduction zone — in this case the Cascadia Subduction Zone — the physical convergence of two tectonic plates that sees one plate, an oceanic plate, submerge under the other, either another oceanic plate or a continental plate.

The result is a highly unstable geographical area that features volcanoes, earthquakes and mountain ranges. The entire Pacific region is lined with these subduction zones, earning it the nickname the Ring of Fire.

The Cascadia Subduction Zone sits a few hundred kilometres off the coast of B.C. and stretches from the middle of Vancouver Island to northern California. It marks the convergence of the submerging Juan de Fuca plate and the North American plate. Movement here could produce an earthquake with a magnitude of 9.0 or greater.

Given their geographical similarities, what was happening in Japan Friday could easily serve as a carbon copy for what would happen in areas along the west coast, in particular Vancouver and Victoria, should there be major movement along the Cascadia subduction.

While the west coast of Vancouver Island should protect Vancouver from the brunt of the ensuing tsunami — which will be moving at speeds of 700 kilometres an hour, the equivalent of a jet — the devastation will still be catastrophic.

The question, then, is: How long before the big one strikes?

“We can’t predict when the next one will occur,” said Clague. “But I would say that they are inevitable. We will experience one and what I’m most interested in is that this earthquake is a perfect analog for what we would expect to see on our coast.”

Clague said geographical evidence suggests there is major movement along the Cascadia subduction about every 400 to 500 years, the last rupture occurring in about 1700 AD. The ensuing earthquake, estimated to be comparable to Thursday’s, is believed to have triggered a tsunami that struck Japan.

Should there be an earthquake, residents along B.C.’s coast would likely have 15 to 20 minutes to find high ground before the tsunami hit.

Clague said the amount of energy released during Japan’s 8.9 quake could be compared to the eruption of Mount St. Helens in 1980, or just slightly less than the annual energy consumption of the United States. Based on similar earthquakes in the past, the number of expected aftershocks could be in the thousands, he said.

Clague said there is likely no link between the earthquake in Japan and New Zealand’s 6.3 quake last month, although there is some recent research that suggests that there could be a relationship between earthquakes in different parts of the world.

“Normally we would say there’s no relation,” he said. “But there is some research that is being done that suggests there could be some subtle linkages.”

Meantime, coastal B.C. residents evacuated by a tsunami alert triggered after the earthquake were expected to return home Friday afternoon after it was found the slight rise in ocean levels posed no significant risk.

Sections of the coast recorded up to a metre increase in water levels but no damage.

Those worried about Canadian friends or family in Japan are welcome to call the Department of Foreign Affairs at 613-943-1055 or 1-800-387-3124.

¶ In Vancouver, Mayor Gregor Robertson issued a release saying the city stands “by the Japanese people as they work to overcome this tragedy.” He said the city’s Urban Search and Rescue Squad, which has, in the past, been deployed to other disaster areas, is “prepared to assist in any way necessary if called upon” by the federal government.

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